This invention relates to improvements in electrical subsystems for vehicle, and to vehicles fitted with an improved electrical subsystem.
In a modern vehicle such as a passenger car or truck, there are many microcontrollers, each of the microcontrollers may control the operation of one or more electrical actuators located at various positions around the vehicle such as an electric motor or pump. They may also, or alternatively, receive signals from one or more sensors located at various locations around the vehicle such as steering angle sensors, motor position sensors, wheel speed sensors and so on. They may also receive input signals from devices such as cameras or radar systems, and output control signals for those devices. It is not unusual for several Electronic Control Units (ECUs) to share information amongst themselves in order to provide the required function of the vehicle. The vehicle speed may be used, for example, by the engine ECU and also the steering ECU.
The ECU is typically grouped together with memory and input ports for receiving signals from sensors and sending signals to actuators in the form of a microcontroller. The microcontroller is then grouped together with physical connectors for connection to actuators and sensors, and the components are then sealed within a housing. The various parts within the housing form an electronic control module. This is shown in FIG. 5 of the drawings.
To allow the various modules to send and receive signals to and from these sensors, actuators and other devices as well as to other ECUs, it is known to fit the vehicle with a communication network, most commonly one of the standards known as a communication bus. The bus comprises a bundle of electrical wires, or sometimes optical fibres, which can carry the various items of information around the vehicle. The bus is a local communications network that allows the microcontrollers and sensors etc to talk to each other. Each module should include at least one bus controller, typically within the housing, that allows the module to transmit and receive signals across the bus.
At the time of writing the most common electrical bus in road-vehicles is the Controller Area Network (CAN)-bus, which is a serial communication protocol bus. In a typical bus, messages are transmitted around the system that are coded with an identifier which is used to denote how a receiver should decode the data being transmitted (into physical parameters for example). Each module only acts upon messages with identifiers for data in which it has an interest. The protocol controls how the signals are transmitted, both in terms of coding and timing and how to deal with possible collisions when multiple modules are trying to send messages at the same time. Other bus protocols are also available—and for any given bus protocol there will be a set of rules defining how the bus controller interfaces with the bus.
In the event of a fault of a microcontroller it is important to ensure that incorrect signals cannot be sent across the network bus. If that were allowed to happen, the safety of the vehicle may be compromised.
In the prior art it is known to shut down the microcontroller of the control module when a fault is detected. The detection of a fault is typically performed by a fault detection unit which may be part of the microcontroller, or may be external, but within the ECU. When a fault is detected by the fault detection module it instructs the microcontroller or network interface to switch off, ensuring the network controller cannot send faulty signals across the network bus.